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Message-ID: <20090126215321.GA20726@lst.de>
Date: Mon, 26 Jan 2009 22:53:21 +0100
From: Christoph Hellwig <hch@....de>
To: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: devpts multiple instances feedback
On Sat, Jan 03, 2009 at 05:15:44PM +0100, Christoph Hellwig wrote:
> This is a little untested patch to massage the mount code into about
> how it should look like:
ping?
>
> Index: linux-2.6/fs/devpts/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/devpts/inode.c 2009-01-03 16:52:22.823672077 +0100
> +++ linux-2.6/fs/devpts/inode.c 2009-01-03 17:14:24.153711598 +0100
> @@ -329,106 +329,6 @@ static int compare_init_pts_sb(struct su
> }
>
> /*
> - * Safely parse the mount options in @data and update @opts.
> - *
> - * devpts ends up parsing options two times during mount, due to the
> - * two modes of operation it supports. The first parse occurs in
> - * devpts_get_sb() when determining the mode (single-instance or
> - * multi-instance mode). The second parse happens in devpts_remount()
> - * or new_pts_mount() depending on the mode.
> - *
> - * Parsing of options modifies the @data making subsequent parsing
> - * incorrect. So make a local copy of @data and parse it.
> - *
> - * Return: 0 On success, -errno on error
> - */
> -static int safe_parse_mount_options(void *data, struct pts_mount_opts *opts)
> -{
> - int rc;
> - void *datacp;
> -
> - if (!data)
> - return 0;
> -
> - /* Use kstrdup() ? */
> - datacp = kmalloc(PAGE_SIZE, GFP_KERNEL);
> - if (!datacp)
> - return -ENOMEM;
> -
> - memcpy(datacp, data, PAGE_SIZE);
> - rc = parse_mount_options((char *)datacp, PARSE_MOUNT, opts);
> - kfree(datacp);
> -
> - return rc;
> -}
> -
> -/*
> - * Mount a new (private) instance of devpts. PTYs created in this
> - * instance are independent of the PTYs in other devpts instances.
> - */
> -static int new_pts_mount(struct file_system_type *fs_type, int flags,
> - void *data, struct vfsmount *mnt)
> -{
> - int err;
> - struct pts_fs_info *fsi;
> - struct pts_mount_opts *opts;
> -
> - printk(KERN_NOTICE "devpts: newinstance mount\n");
> -
> - err = get_sb_nodev(fs_type, flags, data, devpts_fill_super, mnt);
> - if (err)
> - return err;
> -
> - fsi = DEVPTS_SB(mnt->mnt_sb);
> - opts = &fsi->mount_opts;
> -
> - err = parse_mount_options(data, PARSE_MOUNT, opts);
> - if (err)
> - goto fail;
> -
> - err = mknod_ptmx(mnt->mnt_sb);
> - if (err)
> - goto fail;
> -
> - return 0;
> -
> -fail:
> - dput(mnt->mnt_sb->s_root);
> - deactivate_super(mnt->mnt_sb);
> - return err;
> -}
> -
> -/*
> - * Check if 'newinstance' mount option was specified in @data.
> - *
> - * Return: -errno on error (eg: invalid mount options specified)
> - * : 1 if 'newinstance' mount option was specified
> - * : 0 if 'newinstance' mount option was NOT specified
> - */
> -static int is_new_instance_mount(void *data)
> -{
> - int rc;
> - struct pts_mount_opts opts;
> -
> - if (!data)
> - return 0;
> -
> - rc = safe_parse_mount_options(data, &opts);
> - if (!rc)
> - rc = opts.newinstance;
> -
> - return rc;
> -}
> -
> -/*
> - * get_init_pts_sb()
> - *
> - * This interface is needed to support multiple namespace semantics in
> - * devpts while preserving backward compatibility of the current 'single-
> - * namespace' semantics. i.e all mounts of devpts without the 'newinstance'
> - * mount option should bind to the initial kernel mount, like
> - * get_sb_single().
> - *
> * Mounts with 'newinstance' option create a new private namespace.
> *
> * But for single-mount semantics, devpts cannot use get_sb_single(),
> @@ -436,20 +336,43 @@ static int is_new_instance_mount(void *d
> * the most recent mount of devpts. But that recent mount may be a
> * 'newinstance' mount and get_sb_single() would pick the newinstance
> * super-block instead of the initial super-block.
> - *
> - * This interface is identical to get_sb_single() except that it
> - * consistently selects the 'single-namespace' superblock even in the
> - * presence of the private namespace (i.e 'newinstance') super-blocks.
> */
> -static int get_init_pts_sb(struct file_system_type *fs_type, int flags,
> - void *data, struct vfsmount *mnt)
> +static int devpts_get_sb(struct file_system_type *fs_type, int flags,
> + const char *dev_name, void *data, struct vfsmount *mnt)
> {
> + struct pts_mount_opts opts = { 0, };
> struct super_block *s;
> int error;
>
> - s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
> - if (IS_ERR(s))
> - return PTR_ERR(s);
> + if (data) {
> + error = parse_mount_options(data, PARSE_MOUNT, &opts);
> + if (error)
> + return error;
> + }
> +
> + if (opts.newinstance) {
> + /*
> + * Mount a new (private) instance of devpts. PTYs created
> + * in this instance are independent of the PTYs in other devpts
> + * instances.
> + */
> +
> + printk(KERN_NOTICE "devpts: creating new instance\n");
> +
> + s = sget(fs_type, NULL, set_anon_super, NULL);
> + if (IS_ERR(s))
> + return PTR_ERR(s);
> + } else {
> + /*
> + * Mount or remount the initial kernel mount of devpts.
> + *
> + * This type of mount maintains the legacy, single-instance
> + * semantics, while the kernel still allows multiple-instances.
> + */
> + s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
> + if (IS_ERR(s))
> + return PTR_ERR(s);
> + }
>
> if (!s->s_root) {
> s->s_flags = flags;
> @@ -461,46 +384,26 @@ static int get_init_pts_sb(struct file_s
> }
> s->s_flags |= MS_ACTIVE;
> }
> - do_remount_sb(s, flags, data, 0);
> - return simple_set_mnt(mnt, s);
> -}
> -
> -/*
> - * Mount or remount the initial kernel mount of devpts. This type of
> - * mount maintains the legacy, single-instance semantics, while the
> - * kernel still allows multiple-instances.
> - */
> -static int init_pts_mount(struct file_system_type *fs_type, int flags,
> - void *data, struct vfsmount *mnt)
> -{
> - int err;
> -
> - err = get_init_pts_sb(fs_type, flags, data, mnt);
> - if (err)
> - return err;
> -
> - err = mknod_ptmx(mnt->mnt_sb);
> - if (err) {
> - dput(mnt->mnt_sb->s_root);
> - deactivate_super(mnt->mnt_sb);
> - }
> -
> - return err;
> -}
> -
> -static int devpts_get_sb(struct file_system_type *fs_type,
> - int flags, const char *dev_name, void *data, struct vfsmount *mnt)
> -{
> - int new;
>
> - new = is_new_instance_mount(data);
> - if (new < 0)
> - return new;
> + /*
> + * Copy over mount options structure into the superblock.
> + */
> + memcpy(&DEVPTS_SB(mnt->mnt_sb)->mount_opts, &opts, sizeof(opts));
> +
> + error = simple_set_mnt(mnt, s);
> + if (error)
> + return error;
> +
> + error = mknod_ptmx(mnt->mnt_sb);
> + if (error)
> + goto out_dput;
>
> - if (new)
> - return new_pts_mount(fs_type, flags, data, mnt);
> + return 0;
>
> - return init_pts_mount(fs_type, flags, data, mnt);
> + out_dput:
> + dput(mnt->mnt_sb->s_root);
> + deactivate_super(mnt->mnt_sb);
> + return error;
> }
> #else
> /*
---end quoted text---
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